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Chapter 10 - Spinal interneuronal control of the lower urinary tract
Book chapter

Chapter 10 - Spinal interneuronal control of the lower urinary tract

Jaclyn H. DeFinis and Shaoping Hou
Spinal Interneurons, pp 277-295
2023
DOI: https://doi.org/10.1016/B978-0-12-819260-3.00012-3

Abstract

Bladder Micturition Plasticity Sphincter Spinal cord injury
Micturition, or urination, is often thought of as an elementary process. However, this function requires the coordination of several organs in order to efficiently store and release urine. To accomplish this, the lower urinary tract (LUT) system needs precise synergistic activity to coordinate bladder autonomic and external urethral sphincter (EUS) somatic efferents. The coordination of these two muscles is achieved by communication between ascending sensory, descending supraspinal, and local spinal circuits. Previous studies demonstrated that a large number of spinal interneurons are involved in the spinobulbospinal micturition reflex pathways. These interneurons elicit either inhibitory or excitatory modulation over autonomic or motor neurons that innervate the LUT. Traumatic spinal cord injury (SCI) often interrupts micturition reflex pathways, resulting in disordered LUT function. An areflexic bladder arises at the acute stage of upper motor neuron injury. However, spontaneous bladder and sphincter reflexes emerge over time, which is attributed to reorganization of spinal neuronal circuits. As a response to injury, spinal interneurons have a profound role in the neuronal plasticity that arises and participate in the modulation of the reestablished involuntary micturition reflex. However, the bladder does not empty completely due to excessive sphincter activity or dyssynergia that occurs between the detrusor muscle of the bladder and the EUS, in which both muscles contract simultaneously. Currently, the interneuronal mechanisms that regulate the recovered micturition reflex are poorly understood. Some studies have, however, recently shed light on the neuronal network within the spinal cord that controls urinary performance. Here, we review the distribution of spinal interneurons as they relate to LUT function, their proposed role, and the potential for these cells to be used as a therapeutic target to mitigate bladder dysfunction following SCI.

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